This invention relates to a device for detecting large impact, such as, resulting from the collision of a vehicle with another body, and more particularly to an impact detecting device equipped with a movable member (mass) and an elastic member.
In general, when a vehicle collides with another body and hence is decelerated, deceleration of the vehicle and deceleration time vary to a large extent depending on the type of body, with which the vehicle collides. For instance, in case a vehicle collides with a concrete wall, the deceleration of the vehicle is extremely high, and the time lapsed for the vehicle to stop is also extremely short. On the other hand, in case a vehicle collides with a guard rail or other vehicle, the resulting deceleration is relatively low, and the time lapsed for the vehicle to stop is relatively long. Since deceleration varies depending on the type of body, with which a vehicle collides, it is not preferable that the collision of a vehicle be detected by resorting to the deceleration alone. In this sense, there has been developed a collision or impact detecting device, in which an integration of a deceleration resulting from the collision of a vehicle is measured, and then when the integration arrives a given value, a signal is developed. The collision detecting device of the type described includes a movable member (or mass) movable substantially along a straight line from an unactuated position to an actuated position, a spring for resisting the movement of the movable member, and a switch actuated by the movable member, whereby when impact is applied thereto, the movable member moves from its unactuated position to its actuated position, thereby actuating the aforesaid switch. Meanwhile, the duration or time to be lapsed from the collision of a vehicle to the stoppage thereof is as short as 3 to 40 milliseconds. For detecting a collision which causes deceleration only of such a short time, it is mandatory that the spring constant of the spring be lowered. It follows from this that the extent of the movement of the movable member is about 100 mm, and hence the size of the detecting device should be increased, with an additional difficulty of attaching the device to a bumper of a vehicle.